1. Field of the Invention
The present invention relates to an Fe-based sintered alloy valve seat excellent in wear resistance and producing less wear on the valve counterpart of the valve seat.
2. Description of the Related Art
As the technology of sintering has progressed, it has become possible to mass produce various mechanical parts from sintered alloys with good dimensional accuracy. For example, sintered valve seats have been produced.
JP-A 3-158445 discloses a valve seat composed of an Fe-based sintering alloy. The structure of the valve seat is such that hard particles comprising 25-45% by weight of Cr, 20-30% by weight of W, 20-30% by weight of Co, 1-3% by weight of C, 0.2-2% by weight of Si and 0.2-2% by weight of Nb with the balance being Fe and inevitable impurities, and hard particles comprising 25-32% by weight of Mo, 7-10% by weight of Cr, 1.5-3.5% by weight of Si with the balance being Co and inevitable impurities are uniformly dispersed in an Fe-based alloy base in a total amount of 10-25% by weight, wherein the Fe-based alloy base comprises 1-3% by weight of Cr, 0.5-3% by weight of Mo, 0.5-3% by weight of Ni, 2-8% by weight of Co, 0.6-1.5% by weight of C and 0.2-1% by weight of Nb with the balance being Fe and inevitable impurities and has a structure mainly comprising a pearlite phase and a venite phase.
Recently, direct injection engines have been developed and put into practical use in which fuel is directly injected into the combustion chambers. To achieve high-performance, high fuel efficiency and downsizing, these engines have been operated under lean burn conditions by raising the air-fuel ratio. However, this has increased temperatures in the combustion chambers of the engines above those in conventional engines. At such high temperatures, conventional valve seats do not exhibit sufficient wear resistance. The high temperatures also lead to serious wear of the valves that are counterparts to the valve seats.
The present invention provides an Fe-based sintered alloy valve seat made of an Fe-based sintered alloy. In comparison with conventional valve seats, the Fe-based sintered alloy valve seat exhibits remarkable high strength and wear resistance. In addition, valve counterparts to the Fe-based sintered alloy valve seat exhibit remarkably less wear than valve counterparts of conventional valve seats.
The Fe-based sintered alloy in the Fe-based sintered alloy valve seat comprises a base comprising 15-40% by weight of Cu, 0.3-12% by weight of Ni and 0.0005-3.0% by weight of C with the balance being Fe and inevitable impurities. The Fe-based sintered alloy has a structure which comprises an Fe-based alloy phase composed of Fe as a main component combined by a Cu-based alloy phase composed of Cu as a main component, wherein a hard particle phase having Micro Hardness Vickers (xe2x80x9cMHVxe2x80x9d) of 500-1700 is dispersed in the base in an amount of 5-30% by volume while surrounded by the Fe-based alloy phase.
When hard particles including Co and/or Cr are mixed with Fe powder and Cuxe2x80x94Ni alloy powder (or, mixed powder of Ni powder and Cu powder), and further with C powder when necessary, and then the mixed powder is pressed, followed by sintering, a part of Co and/or Cr included in the hard particles diffuses in the base obtained from the Fe powder and Cuxe2x80x94Ni alloy powder, including C powder when necessary, and a base is formed which comprises 15-40% by weight of Cu, 0.3-12% by weight of Ni, 0.0005-3.0% by weight of C, and 0.1-10% by weight of Co and/or 0.1-10% by weight of Cr.